- Haskell-Cafe - Haskell.org

HGamer3D - 0.3.x - Building Fixed
by Peter Althainz 02 Apr '14

02 Apr '14

Dear All, I recognized that there were some serious bugs in build code for HGamer3D, which basically prevented building it successfully. I'm very sorry for this! As always there are some explanations how this could happen, but anyhow, I could imagine how frustrating it is to try, spend time and then: no success. This has been fixed now. The detailed build instructions on http://www.hgamer3d.org/Install.html do work, they have been tested on 4 different linux distros and Windows exactly the way described there. regards Peter

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New GHC Features for 7.10.1 and Beyond
by Gershom Bazerman 01 Apr '14

01 Apr '14

There's been lots of exciting work going into the forthcoming GHC 7.8.1 release. But even with all these new features, our language is far from complete and I wouldn't want the GHC team to rest on their laurels. Especially with so much renewed community involvement in GHC development, it seems appropriate to share some ideas some of us have been discussing for future releases, and take a poll of community consensus regarding which ones people might be excited to jump in and help out with, or might find particularly helpful. One important area that needs work is exceptions. These are famously difficult, and many libraries have been written to provide checked exceptions, or unify error and exceptions in various ways. It seems to me that the problem, all along, has been that we've decided to give Haskell _imprecise exceptions_ with special semantics. It would alleviate a great deal of confusion if we implemented a -fprecise-exceptions flag that remedied this. Additionally, while we have long known that Haskell is not a "lazy" language but a "non-strict" one, our leading compiler only rarely takes advantage of this. It is well known that for every program there is a reduction strategy that preserves non-strict semantics while using as few reductions as possible. This is known as the "optimal reduction" strategy, and it is calculable and well understood. We should put some work into a -foptimal-reduction flag. Another important area of research is quantum computation. The D-Wave Two, with 512 qbits, is a commercially available quantum computer now deployed in a few leading institutions. As more and more people begin to purchase D-Wave systems for home hacking, every language worth its salt will need to be able to target this system. Now that cross compilation is more fully supported, it would be good to start putting work into a dwave backend. We've also seen a lot of interest in distribution and cloud computing. From the articles I've read, efficient concurrent programming involves using node.js, so I think we should put some work into writing a new-new-new-IO Manager built on top of this technology. Furthermore, it's ridiculous that while Haskell allows simple concurrent and distributed programming, it offers no simple way to set up a distributed environment. Work should be put into a compiler mode that provisions cloud resources automatically and distributes the target binary among them, with a flag such as: -fvia-s3 _credit_card_number_ There are a few cases where a good idea in GHC can be taken further, and I don't know why we haven't tried already. For example, we've found that despite introducing some occasional problems, the state hack also has drastically improved performance. Since it works so well, we should provide a dual to -fno-state-hack, -fmore-state-hack, for those who really need every last drop of performance. Similarly, now we have type holes that let us see what types should be inserted in various spots. -fvalue-holes is the next logical step, to tell us what terms we should be writing. Also, while we've put so much emphasis on correctness, we've also loosened the bolts optionally the other way, with flags such as -XIncoherentInstances. Along the same lines, I would like to introduce -XImpossibleInstances to let us express such useful things as "instance Int String," "instance IO Comonad," and "instance data if". -fdefer-type-errors allows us to defer type errors to runtime. Having spent some time with JavaScript lately, I think this doesn't go nearly far enough. It would be good to run programs with other sorts of problems as well, for educational purposes and for quick hacking. So work should be put into a -fdefer-scope-errors flag, as well as -fon-error-resume-next, which has done wonders for the resilience of Visual Basic code (see also the wildly useful ability to set the top level error handler in PHP). With all these features put together, we have a powerful new way to approach Haskell programming, and it would be good to enable them by default on .ilhs files (illiterate haskell). It also was pointed out to me recently by Jason Dagit that while we have had debates and confusion over closed and open type families and functions for years, topologists have solved this problem elegantly. With some basic point set topology under one's belt, a -XClopenTypeFamilies extension seems almost trivial to implement. Finally, I'm very sorry to see that my proposal for youtube syntax has languished, and I hope it can be revived: http://www.haskell.org/pipermail/haskell-cafe/2012-April/100527.html HTH HAND, Gershom

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[TFPIE2014] final call for papers
by Peter Achten 01 Apr '14

01 Apr '14

3rd International Workshop on Trends in Functional Programming in Education (TFPIE 2014) May 25, 2014 Utrecht University Soesterberg, The Netherlands (http://www.cs.uwyo.edu/~jlc/tfpie14/) The 3rd International Workshop on Trends in Functional Programming in Education, TFPIE 2014, will be co-located with the Symposium on Trends in Functional Programming (TFP 2014) at Soesterberg, at the “Kontakt der Kontinenten” hotel in the Netherlands on Sunday, May 25th. TFP will follow from May 26-28. The goal of TFPIE is to gather researchers, teachers and professionals that use, or are interested in the use of, functional programming in education. TFPIE aims to be a venue where novel ideas, classroom-tested ideas and work-in-progress on the use of functional programming in education are discussed. The one-day workshop will foster a spirit of open discussion by having a review process for publication after the workshop. The program chair of TFPIE 2014 will screen submissions to ensure that all presentations are within scope and are of interest to participants. Potential presenters are invited to submit an extended abstract (4-6 pages) or a draft paper (up to 16 pages) in EPTCS style. The authors of accepted presentations will have their preprints and their slides made available on the workshop's website/wiki. Visitors to the TFPIE 2014 website/wiki will be able to add comments. This includes presenters who may respond to comments and questions as well as provide pointers to improvements and follow-up work. After the workshop, presenters will be invited to submit (a revised version of) their article for review. The PC will select the best articles for publication in the journal Electronic Proceedings in Theoretical Computer Science (EPTCS). Articles not selected for presentation and extended abstracts will not be formally reviewed by the PC. TFPIE workshops have previously been held in St Andrews, Scotland (2012) and in Provo Utah, USA (2013). ** Invited Speaker ** TFPIE is pleased to announce that professor Johan Jeuring of Utrecht University and Open University, both in The Netherlands is giving an invited talk entitled: "Automatic tutoring and assessing functional programs". ** Program Committee ** James Caldwell, (Program Chair) University of Wyoming Peter Achten, Radboud University, Nijmgen Edwin Brady, University of St Andrews, St Andrews Jurriaan Hage, Universiteit Utrecht Philip Holzenspies, University of Twente Daniel R. Licata, Wesleyan University Marco T Morazan, Seton Hall University Christian Skalka, University of Vermont David Van Horn, Northeastern University ** Submission Guidelines ** There will be two types of presentations at TFPIE 2014. Regular papers and “best lecture” presentations. The best lecture talks are intended to allow for presentations or short lectures of purely pedagogical material. Papers and abstracts can be submitted via easychair at the following link: https://www.easychair.org/conferences/?conf=tfpie2014 ** Papers ** TFPIE 2014 welcomes submissions describing techniques used in the classroom, tools used in and/or developed for the classroom and any creative use of functional programming (FP) to aid education in or outside Computer Science. Topics of interest include, but are not limited to: * FP and beginning CS students * FP and Computational Thinking * FP and Artificial Intelligence * FP in Robotics * FP and Music * Advanced FP for undergraduates * FP in graduate education * Engaging students in research using FP * FP in Programming Languages * FP in the high school curriculum * FP as a stepping stone to other CS topics * FP and Philosophy ** Best Lectures ** In addition to papers, this year we are requesting “best lecture” presentations. What’s your best lecture topic in an FP related course? Do you have a fun way to present FP concepts to novices or perhaps an especially interesting presentation of a difficult topic? In either case, please consider sharing it. Best lecture topics will be selected for presentation based on a short abstract describing the lecture and its interest to TFPIE attendees. ** Important Dates ** * 1 February 2014: TFPIE submissions open on easychair. * 14 April 2014: Early registration for TFP closes * 21 April 2014: Submission deadline for draft TFPIE papers and abstracts * 27 April 2014: Notification of acceptance for presentation * 15 May 2014: Registration for TFPIE closes - as does late registration for TFP * 25 May 2014: Presentations in Soesterberg, Netherlands * 29 June 2014: Full papers for EPTCS proceedings due * 16 August 2014: Notification of acceptance for proceedings * 8 September 2014: Camera ready copy due for EPTCS Submission of an abstract implies no obligation to submit a full paper; abstracts with no corresponding full versions by the full paper deadline will be considered as withdrawn. At least one author from each accepted presentation must attend the workshop.

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Problems with Network/MVar
by Pierre-Étienne Meunier 01 Apr '14

01 Apr '14

Hello cafe, I’m trying to run a server to synchronize a bunch of machines, and one of the threads keeps crashing every ~50 hours. One of the threads is an HTTP server and stays alive forever, so it’s not a Unix signal problem. I don’t have much information on its stdout/stderr, and the bug is not very reproducible, since it can happen even though very few of its maximum ~200 clients are connected. Is there a reason why the following can stop after some time? server::Config -> MVar State -> IO () server config state=withSocketsDo $ do installHandler sigPIPE Ignore Nothing threads<-Sem.new $ maxThreads config forever $ do E.catch (bracket (listenOn $ port config)) sClose $ \sock->forever $ do (s,a,_)<-accept sock wait threads forkIO $ (reply state s a)`finally`(signal threads)`E.catch`(\e->let _=e::IOException in return ()) (\e->let _=e::IOException in return ()) threadDelay 100000 This was compiled with GHC 7.6.3, -threaded and run on Debian Jessie (I have not tested other settings), and Config and State are both record types. Thanks, Pierre

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[TFP2014] First Call for Participation
by Peter Achten 01 Apr '14

01 Apr '14

--------------------------------- 1ST CALL FOR PARTICIPATION --------------------------------- ======== TFP 2014 =========== 15th Symposium on Trends in Functional Programming May 26-28, 2014 Utrecht University Soesterberg, The Netherlands http://www.cs.uu.nl/wiki/TFP2014/WebHome Registration is now open for the symposium on Trends in Functional Programming (TFP). It is an international forum for researchers with interests in all aspects of functional programming, taking a broad view of current and future trends in the area. It aspires to be a lively environment for presenting the latest research results. Submission for TFP is now closed, and the complete programme (29 presentations and two invited talks) for TFP can be perused here: http://www.cs.uu.nl/wiki/TFP2014/PresentationSchedule TFP 2014 will be the main event of a pair of functional programming events. The other is the International Workshop on Trends in Functional Programming in Education (TFPIE). TFPIE will take place on May 25th. Its website is located at http://www.cs.uwyo.edu/~jlc/tfpie14/ . The submission deadline for TFPIE is April 21, 2014. INVITED SPEAKERS TFP is pleased to announce talks by the following two invited speakers: John Hughes of Chalmers, Goteborg, Sweden, is well-known as author of Why Functional Programming Matters, and as one of the designers of QuickCheck (together with Koen Claessen); the paper on QuickCheck won the ICFP Most Influential Paper Award in 2010. Currently he divides his time between his professorship and Quviq, a company that performs property-based testing of software with a tool implemented in Erlang. Geoffrey Mainland received his PhD from Harvard University where he was advised by Greg Morrisett and Matt Welsh. After a two year postdoc with the Programming Principles and Tools group at Microsoft Research Cambridge, he is now an assistant professor at Drexel University. His research focuses on high-level programming language and runtime support for non-general purpose computation. IMPORTANT DATES Early registration: April 14, 2014 Late registration: May 15, 2014 TFPIE Workshop: May 25, 2014 TFP Symposium: May 26-28, 2014 Registrations can be made at the following URL: http://www.cs.uu.nl/wiki/TFP2014/Register This page will also point you to the web page of the venue where you can arrange for your stay. hoping to see you there. Jurriaan Hage (General Chair)

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Re: [Haskell-cafe] Haskell Weekly News
by Roman Cheplyaka 01 Apr '14

01 Apr '14

(This was submitted to glasgow-haskell-users, probably by mistake. Redirecting to cafe.) * harry <voldermort(a)hotmail.com> [2014-03-31 00:36:10-0700] > There hasn't been a HWN since mid-December. I've emailed the editor with no > response, and there doesn't seem to have been any (public) online activity > from him since. > > I hope he's OK, but either way, it seems that HWN needs a new editor. Any > volunteers? While we're at it, I suggest to potential editors to look up how HWN looked back when Brent Yorgey was the editor. IMO it was much more interesting to read than a mechanically compiled list of reddit and SO posts which HWN has become lately. That style is more time and effort consuming, though. (http://ro-che.info/ccc/06) Roman

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groupBy without Ord?
by martin 01 Apr '14

01 Apr '14

Hello all, when I groupBy a list in order to cluster elements which satisfy some sort of equality, I usually have to sort the list first, which requires Ord. However groupBy itself does not require Ord, but just Eq. How can I groupBy a List whose elements are only instances of Eq but not of Ord?

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Re: [Haskell-cafe] Groundhog - Given entity, how to retrieve autokey value?
by lykahb＠gmail.com 01 Apr '14

01 Apr '14

Hi Ross, The primary key if it is generated by a database is not part of the entity. However, you can store it in your entity if you supply it yourself. It is a good approach if your entity has a natural primary key (like username). Only default key can be auto-incremented. Here is more detailed description of how keys work in Groundhog https://www.fpcomplete.com/user/lykahb/groundhog#keys-and-references Also you may want to use project instead of select. For example, "project (AutoKeyField, MyConstructor) $ MyField ==. myValue" would return id and the entity. Thank you, Boris Lykah On Sunday, March 30, 2014 12:41:40 AM UTC-4, Ross Pokorny wrote: > > Hello, > > I am trying to build a RESTful web application using Groundhog for > persistence. In order to generate URLs for my entities (e.g. for the > Location HTTP header), I need a way, given that I have an entity, to obtain > its id (its AutoKey). From what I've gathered so far, in normal Groundhog > usage, the primary key is not part of the actual entity datatype. The only > place where I've seen it returned is from the 'insert' functions in > Database.Groundhog. I need the id in cases where I have retrieved an > already-existing entity using 'select', but I cannot find a way to obtain > it. > > I gather that this might not be possible with the current API, and that > instead, I may need to explicitly define a field on the entity type to > store the id instead of using the auto-generated field that Groundhog > normally provides. In that case, my question is how do I set up that field > to be an auto-incrementing key, and not simply a value with a unique > constraint. Also, would Groundhog recognize that field as the AutoKey, and > would it return it from 'insert' calls? > > Thanks, > > Ross Pokorny >

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Re: [Haskell-cafe] [ANN] network-transport-zeromq-0.1.
by Patrick Wheeler 01 Apr '14

01 Apr '14

> Our vision is that send/expect should work according to the default distributed-process semantics, but one ought to be allowed to vary the semantics of channel-based communication (as opposed to actor-based) according to what is relevant to the application. E.g. an application ought to be able to give up reliability for better latency/throughput on a channel-by-channel basis. That pretty exciting. I will have to put aside some time to tryout Cloud Haskell on top of your ZeroMQ layer. I would love to see a simple example of how this would work with different reliability settings in a ping-pong example. On Mon, Mar 31, 2014 at 1:34 PM, Edsko de Vries <edsko(a)well-typed.com>wrote: > Hi Mathieu, > > That sounds great! It's great to see that the redesign of Cloud Haskell > with a pluggable Network.Transport layer is in fact being used. Good stuff! > > Edsko > > -- > You received this message because you are subscribed to the Google Groups > "parallel-haskell" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to parallel-haskell%2Bunsubscribe(a)googlegroups.com. > For more options, visit https://groups.google.com/d/optout. > -- Patrick Wheeler Patrick.John.Wheeler(a)gmail.com Patrick.J.Wheeler(a)rice.edu Patrick.Wheeler(a)colorado.edu

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ghc-mod v4.0.0
by Kazu Yamamoto 31 Mar '14

31 Mar '14

Hello, I'm happy to announce the release of ghc-mod v4.0.0. You can see its changelog here: http://hackage.haskell.org/package/ghc-mod-4.0.0/changelog This version provides an interactive command called ghc-modi. As you can guess, this makes syntax error highlighting much faster. The Emacs front-end resolves the "import hell". If you are an Emacs user, probably it is worth reading this page: http://mew.org/~kazu/proj/ghc-mod/en/emacs.html The entire documentation was re-written. Please give a look at it if you are interested: http://mew.org/~kazu/proj/ghc-mod/en/ P.S. This is not April fool. --Kazu

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